a) Field of the Invention
The present invention relates to high-intensity discharge lamps, and particularly, to high-intensity mercury and metal halide lamps.
b) Problems in the Art
High-intensity discharge or arc lamps such as mercury lamps and metal halide lamps represent an efficient, high-intensity source of light, particularly for high-intensity, large quantity, or large area of lighting. There are different types of arc lamps in general, and mercury and metal halide arc lamps in particular, such as are available from a wide variety of manufacturers and distributors.
Conventional lamps of this type generally consist of a mounting apparatus, such as a screw-end or threaded end, an arc tube, electrical connections connected between the screw-end and the arc tube, and a glass jacket, outer envelope, or bulb surrounding the arc tube and at least some of the electrical connections.
As can be appreciated, and as is known to those of ordinary skill in the art, the arc tube is generally an elongated envelope made of quartz or some other high-temperature resistant yet substantially transparent material. The arc tube thus generally has a longitudinal axis which is generally aligned along the longitudinal axis of the entire arc lamp, which in the case of an arc lamp with a threaded end, extends between the screw-end and the opposite end of the lamp.
The arc tube is generally evacuated of air and is loaded with chemicals, including mercury or metal halides in mercury and metal halide lamps, which facilitate creation of a high-intensity light discharge arc between electrodes which extend into the arc tube, when electricity is applied to the electrodes. The bulb is also usually evacuated to provide temperature insulation and to provide protection to the arc tube.
Because the arc tube of such conventional arc lamps is aligned along the longitudinal axis of the arc lamp, the lighting characteristics of these conventional arc lamps are somewhat uniform. Most of the light emanating from such an arc tube does so laterally (perpendicularly from the longitudinal axis), with a much less significant amount of light emanating from the arc tube's opposite ends. The light pattern which is emitted from these conventional arc lamps, while being somewhat consistent between conventional arc lamps, does lack flexibility and can present limitation as to the light pattern radiated from the lamp.
In most lighting applications, reflectors or reflecting elements are utilized to alter the light pattern emanating from the lamp. Hemispherical reflectors which are symmetrical around the longitudinal axis of the arc lamp are a conventional choice. The arc lamp is screwed into a socket and seats within the reflector so that its outer end points to the lighting target. Therefore, a substantial amount of the light emanating from the lamp and reflector combination is reflected light originally emanating from the sides of the arc tube, gathered in the reflector, and then redirected.
It is well known that direct light is more efficient than reflected light. Any reflection results in some light loss. A conventional arc lamp having the arc tube aligned along the lamp's longitudinal axis, and positioned in a conventional symmetrical reflector, results in a significant amount of light loss.
Furthermore, there is an effect which is known as "tilt factor" which can reduce the efficacy (lumens per watt) of metal halide or mercury arc lamps. An arc lamp operates with the highest efficacy when the arc tube is positioned vertically. The next best positioning of an arc tube as far as efficacy is concerned would be when the arc tube is horizontal. High temperatures during operation of an arc lamp cause evaporation of chemicals within the arc tube which in turn causes the gas discharge which emits light. If there is uneven heating within the arc tube, which renders some locations sufficiently cooler from others, the efficacy of the lamp will decrease. Chemicals may condense out blocking light from emanating from the arc tube. Precipitation of these essential chemicals also means that they will not be discharging light.
Therefore, traditionally, these arc lamps have been desired to be installed and operated in a directly vertical fashion. Since the arc tube is aligned along the longitudinal axis of the lamp, and the aiming axis of the lamp is vertical, optimal efficacy is achieved. U.S. Pat. No. 4,341,975, by Phillipp, et al., entitled "Jacketed Lamp Having Transversely Mounted Arc Tube", issued Jul. 27, 1982, discusses this phenomenum. In that patent, it is recognized that arc lamps are not always desired to be positioned in a directly vertical orientation. The Phillipp patent therefore presents a method by which the bulb of the arc lamp can be positioned horizontally, and yet the arc tube itself is positioned vertically for optimal efficacy.
In many lighting applications, however, the aiming direction of the arc lamp is other than completely vertical or completely horizontal. In those conditions, a conventional mercury or metal halide arc lamp with the arc tube aligned along the longitudinal axis, loses efficacy. Because heat rises, tilting of the arc tube between horizontal and vertical (in any direction), will cause hotter areas to develop at the highest point of the arc tube, generally along the top of the arc tube. In turn, cooler areas will develop at the lowest points, generally along the lower part of the arc tube. These temperature differences, even though the overall temperature through and surrounding the arc tube is quite high, can cause precipitation of some of the loaded chemicals inside the arc tube. Such precipitation will cause clouding and blockage of light, and of course, will also make less chemical available for production of the arc stream, which will also contribute to a reduction in the amount of light possible from the arc lamp. Other detrimental results can be drops in wattage of the lamp of, for example, three or four percent, and pressure changes in the lamp; all of which can adversely affect the consumption of power by the lamp, making it less efficient and less economical.
This problem is called the "tilt factor". If a conventional mercury or metal halide arc lamp is tilted below horizontal, generally between 0.degree. and 45.degree. below horizontal, the tilt factor results in light output loss of up to 20%.
Therefore, there is a lack of flexibility in such arc lamps having the arc tube aligned directly along the longitudinal axis of the arc lamp. Furthermore, conventional such arc lamps suffer from the tilt factor, which can produce serious efficiency and efficacy problems.
It is therefore a principal object of the present invention to provide a tilted arc discharge lamp which can increase efficacy or light output, efficiency, and flexibility of use of an arc lamp to improve upon or solve deficiencies and problems in the art.
A further object of the present invention is to provide a lamp as above described with respect to mercury and metal halide lamps which can be utilized to solve tilt factor problems, light direction problems and other lighting deficiencies or limitations.
A further object of the present invention is to provide a lamp as above described which can be utilized in existing bulbs or glass jackets and screw-in mounts.
Another object of the present invention is to provide a lamp as above described which can be advantageously combined with reflector assemblies to increase the amount of light and allow improved flexibility in directing light.
A further object of the present invention is to provide a lamp as above described which is efficient, and economical to manufacture, install, and maintain.
These and other objects features and advantages of the present invention will become more apparent with reference to the accompanying drawings and specification.